USA 193 Post-Shootdown Analysis

Coverage started 2008 February 27

Updated 2009 May 26

On 2008 February 21, the US Department of Defense
reported
the successful intercept of USA 193 by an SM-3 missile launched from the USS
Lake Erie, positioned northwest of Hawaii. The missle was launched at on 2008
February 20 at approximately 22:26:47.36 EST (2008 February 21 at 03:26:47.36
UTC).

The following NOTAM (NOtice To AirMen) was released on the Defense Internet NOTAM
Service prior to the event restricting the area to be used for launch:

The restricted area and time agreed well with orbital data released on the SeeSat
list just prior to the intercept. I am providing an STK Viewer file (see
bottom of this page for more information on STK Viewer)
which shows the area restricted by the NOTAM and the SeeSat orbit of USA 193
during the NOTAM period to illustrate the agreement.

The Viewer file shows the NOTAM area to an altitude of 300 km and the green
dashed line is the ground track of USA 193. The position of USA 193 is also
shown. Based on the video of the intercept from the Satellite
Shootdown Briefing given by Gen Cartwright on Feb 21, the position of the
observing plane and its heading is shown at the time of launch.

Note that the observing aircraft is flying along the boundary of the NOTAM
area, just outside the restricted area and looking at the USS Lake Erie just
inside the restricted area. Using the pointing angles of the video sensor, seen
at the bottom of the video, the position of the USS Lake Erie is determined to
be 23.48137 N, 163.28272 W, about 23 km from the aircraft.

Screen shot from STK Viewer file of Video View of USS Lake Erie

From the video, it appears that the SM-3 launch occurred at 03:26:47.36 UTC,
38.5 seconds after USA 193 rose above the horizon as seen from the USS Lake
Erie.

Screen shot from STK Viewer file of Engagement Geometry at Time of SM-3 Launch

On 2008 February 27, Air Force Space Command began releasing orbital data
labeled as "USA 193 DEB" via the Space
Track web site (which requires a user account to access). As of this update,
orbital data (TLEs) has been released for 173 pieces of debris (they still have
not released any TLEs for the original satellite, however, which is still shown
to be in orbit). An initial analysis of this debris is unable to determine an
intercept time, due to the poor quality of the data. However, according to a
story
in the Omaha World-Herald, the intercept occurred approximately 170 seconds
after launch (roughly 03:29:35 UTC).

A check of the Gabbard plot for this event
shows debris ranging from 147 km altitude at perigee all the way up to 2,689 km
at apogee. Of particular concern, however, is that the relatively small number of
conjunctions (close approaches within 5 km of a satellite on orbit) reported for
this debris so far has included satellites such as LANDSAT 5 and 7, SPOT 5,
SAR-LUPE 3, QUICKBIRD 2, OFEQ 7, METOP-A, TIMED, WORLDVIEW-1, TERRA, GRACE-1 and
-2, ENVISAT, IKONOS 2, several Iridium and Orbcomm satellites, and even the
International Space Station and ATV-1 (Jules Verne). For the latest conjunction
report, please check
SOCRATES.

Screen shot from STK Viewer file of Debris Orbits at Time of SM-3 Launch

Analysis of the orbital lifetime of this debris is particularly difficult, too.
According to open sources, the original USA 193 spacecraft was approximately 4.6 m
long and 2.4 m wide. Assuming a cylindrical shape, that would give it a volume of 21.4
cubic meters. Those same sources reported a mass (presumably including the hydrazine
fuel) of 5,000 lbs or 2,300 kg. Subtracting out the fuel, reported by the US DOD as
1,000 lbs, would yield a dry mass of about 1,800 kg. That would yield an average
density of 85 kg/m3.

Reports by the US DOD cite
"no
parts larger than a football survived the strike." A regulation NFL football
is 11 inches long and 21 inches in circumference, so the diameter of a sphere
with the same volume works out to about 20 cm. Since the US Space Surveillance
Network typically cannot track objects smaller than 10 cm, these USA 193 debris
pieces should range from 10–20 cm in diameter. Assuming these are spheres,
the total mass of the pieces cataloged so far (using the average density of the
original spacecraft) would be between 7.7 kg and 61.9 kg—or only 0.4 to 3.4
percent of the original dry mass.

Assuming this information is correct and using the same approach as applied
to the analysis of the orbital debris of from the Chinese ASAT test, we obtain the following chart. It
shows the percent of the 174 objects which decay over time (at least 152 of
which are reported to have already decayed), based on our analysis. The black
line represents 10-cm objects and the blue line represents 20-cm objects. In the
10-cm case, the last object decays 81 days after the intercept; in the 20-cm
case, the last object decays 99 days after the intercept (these estimates do not
include the original piece for which we have no TLE data). If any of the pieces
are larger than reported, they will take progressively longer to decay. (Note:
the 'glitch' above 85 percent is the result of debris pieces still being shown
as in orbit, according to the NORAD catalog, but which our calculations show
should already have decayed. The data below 85 percent is based on reported
decay dates and suggests that our calculations might be optimistic or the pieces
might be larger than reported.)

For comparison, we provide our original analysis, based on the first data
available for each debris object, in the figure below. The current data shows
the decay to be taking somewhat longer than originally estimated but far closer
than the 40-day estimate initially provided by the US Department of Defense.

This analysis will be updated as additional information becomes available.

Note: Larger versions of all the images provided on this page are available
by clicking the images. The interactive STK Viewer files of these scenes are
also provided to give you a far better sense of the overall environment by
allowing you to zoom in and out and move around the Earth while watching all the
satellites moving in their orbits.

Note:STK Viewer is a free product which allows anyone
with a Windows computer to view an STK (System Tool Kit) scenario. With it,
you can animate a scenario forward or backward, pause the animation, and zoom or
pan the view for a more complete understanding of the event. Just like with
Adobe Acrobat, where the authoring software requires a license but the Adobe
Reader is free, STK can produce STK Viewer files—also known as
VDFs—which can then be viewed by anyone with the STK Viewer software. You
can find the free STK Viewer on CelesTrak here. - TS